Determine the concentrations of a selected group of constituents in breast tissue obtained at mastectomy and to assay for these same substances in the serum of the patients obtained before their surgery and then sequentially on a scheduled basis over a period of time. Our aim is to find a constituent in cancerous breast tissue that is present in a concentration different from that in normal breast tissue and then to try to establish if changes in these concentrations in the breast tissue are reflected in the serum and whether the course of the disease is reflected in the serum pattern. We are now routinely obtaining in our laboratory breast tissue for analysis of estrogen receptor protein. It is our aim to determine in the cytosol and pellet of these tissues a variety of substances whose assays are in use in our laboratory. In addition, we can make available specimens for analysis in other laboratories